Today the IEEE 1149.1 (JTAG) Test Access Port (Tap) interface is used for many different applications. While initially designed to provide a serial test interface on ICs to facilitate board testing, the Tap interface now serves as a serial interface for additional IEEE standards for such things as emulation, trace, and debug (IEEE 5001) of ICs and cores, mixed signal testing (IEEE 1149.4) of ICs and cores, advanced IC to IC interconnect testing (IEEE 1149.6), embedded core testing (IEEE 1500), and in-system-programming of circuits in ICs and cores (IEEE 1532).
An IC device may contain many embedded 1149.1 based Tap architectures (Tap domains). Some of these TAP domains are associated with intellectual property (IP) core circuit devices within the IC, and serve as access interfaces to test, debug, trace, emulation, and in-system-programming circuitry within the IP cores. Other TAP domains may exist in the IC which are not associated with cores but rather to circuitry in the IC external of the cores. Further, the IC itself will typically contain a TAP domain for operating IC level test, debug, trace, emulation, and in-system-programming, as well as the boundary scan register associated with the IC's input and output terminals.
From the above, it is clear that Tap domains are being used in ever growing numbers in devices, such as ICs and cores, for test, debug, trace, emulation, in-system-programming, and other types of operations.